Non-disruptive migration of NVMe-of attached virtual volumes using log-based signaling and confirmation for cutover

Abstract

A virtual volume (vVol) is non-disruptively migrated from a first data storage appliance (DSS) to a second DSS. In a synchronizing phase, data is copied from a source vVol to a destination vVol which is not mapped and to which a host computer has no path. Upon completion of synchronization, (1) a mapping is created to the destination vVol for the host and signaled to the host by sending a notification having an associated log page, (2) it is determined whether the host has retrieved the log page, (3) in response the host retrieving the log page, a cutover is performed making the destination vVol accessible to the host and the source vVol inaccessible to the host, and (4) in response to the host not retrieving the log page, the cutover is not performed, leaving the destination vVol inaccessible to the host computer (migration may be aborted or retried).

What is claimed is: 
     
       1. A method of non-disruptively migrating a virtual volume from a first data storage appliance to a second data storage appliance in a federated multi-appliance data storage system providing data storage services to a virtual-computing host computer, comprising:
 in a synchronizing phase, copying data from a source virtual volume of the first data storage appliance to a destination virtual volume of the second data storage appliance, the destination virtual volume being not mapped and the host computer having no path to the destination virtual volume during the synchronizing phase; and 
 upon completing the synchronizing phase, (1) creating a mapping to the destination virtual volume for the host computer and signaling the mapping to the host computer by sending a notification, the notification having an associated log page retrievable by the host computer, (2) determining whether the host computer has subsequently retrieved the log page, (3) in response to determining that the host computer has subsequently retrieved the log page, performing a cutover operation making the destination virtual volume accessible to the host computer and making the source virtual volume inaccessible to the host computer, and (4) in response to determining that the host computer has not subsequently retrieved the log page, refraining from performing the cutover operation thereby leaving the destination virtual volume inaccessible to the host computer. 
 
     
     
       2. The method of  claim 1 , wherein signaling the mapping to the host computer includes sending an asynchronous event notification (AEN) to which the host computer responds by retrieving the log page. 
     
     
       3. The method of  claim 2 , wherein the asynchronous event notification and the log page retrieval are used as part of Asymmetric Namespace Access (ANA) functionality. 
     
     
       4. The method of  claim 3 , wherein creating and signaling the mapping includes (i) performing a state change, by moving the source and destination virtual volumes to a designated ANA Group Change, of all controllers of the first and second data storage appliances, and (ii) signaling the host computer of the state change using the AEN and associated log page. 
     
     
       5. The method of  claim 3 , wherein multiple host-associated virtual volumes (vVols) are migrated concurrently, and further including, to manage potential race conditions between AENs and log accesses, (1) when a first AEN is sent on a controller of the host computer, temporarily disabling the AEN sending for the host computer until the first AEN is resolved, (2) including in the log file respective identifications of any additional vVols that have become ready for cutover while the AEN sending is disabled, so that the host computer receives notification of the additional vVols when retrieving the log page in response to the first AEN, and (3) when the host computer retrieves the log page, then enabling the AEN sending for the host computer to enable additional AENs to be sent to the host computer for other vVols that subsequently become ready for cutover. 
     
     
       6. The method of  claim 5 , wherein determining whether the host computer has retrieved the log page includes querying all controllers to verify that the AEN sending is enabled. 
     
     
       7. The method of  claim 1 , performed as part of a migration session, and further including, upon creation of the migration session, (1) checking the host computer's connectivity to the second data storage appliance prior to the synchronizing phase, to ensure that controllers exist on the second data storage appliance and have been discovered by the host computer, and (2) creating the destination virtual volume without mapping it to the host computer, so that the destination virtual volume remains inaccessible to the host computer until the cutover operation. 
     
     
       8. A federated multi-appliance data storage system configured and operative to provide data storage services to a virtual-computing host computer, the data storage services including non-disruptively migrating a virtual volume from a first data storage appliance of the system to a second data storage appliance of the system by:
 in a synchronizing phase, copying data from a source virtual volume of the first data storage appliance to a destination virtual volume of the second data storage appliance, the destination virtual volume being not mapped and the host computer having no path to the destination virtual volume during the synchronizing phase; and 
 upon completing the synchronizing phase, (1) creating a mapping to the destination virtual volume for the host computer and signaling the mapping to the host computer by sending a notification, the notification having an associated log page retrievable by the host computer, (2) determining whether the host computer has subsequently retrieved the log page, (3) in response to determining that the host computer has subsequently retrieved the log page, performing a cutover operation making the destination virtual volume accessible to the host computer and making the source virtual volume inaccessible to the host computer, and (4) in response to determining that the host computer has not subsequently retrieved the log page, refraining from performing the cutover operation thereby leaving the destination virtual volume inaccessible to the host computer. 
 
     
     
       9. The federated multi-appliance data storage system of  claim 8 ,
 wherein signaling the mapping to the host computer includes sending an asynchronous event notification (AEN) to which the host computer responds by retrieving the log page. 
 
     
     
       10. The federated multi-appliance data storage system of  claim 9 , wherein the asynchronous event notification and the log page retrieval are used as part of Asymmetric Namespace Access (ANA) functionality. 
     
     
       11. The federated multi-appliance data storage system of  claim 10 , wherein creating and signaling the mapping includes (i) performing a state change, by moving the source and destination virtual volumes to a designated ANA Group Change, of all controllers of the first and second data storage appliances, and (ii) signaling the host computer of the state change using the AEN and associated log page. 
     
     
       12. The federated multi-appliance data storage system of  claim 10 , wherein multiple host-associated virtual volumes (vVols) are migrated concurrently, and wherein the migrating includes, to manage potential race conditions between AENs and log accesses, (1) when a first AEN is sent on a controller, temporarily disabling the AEN sending for the host computer until the first AEN is resolved, (2) including in the log file respective identifications of any additional vVols that have become ready for cutover while the AEN sending is disabled, so that the host computer receives notification of the additional vVols when retrieving the log page in response to the first AEN, and (3) when the host computer retrieves the log page, then enabling the AEN sending for the host computer to enable additional AENs to be sent to the host computer for other vVols that subsequently become ready for cutover. 
     
     
       13. The federated multi-appliance data storage system of  claim 12 , wherein determining whether the host computer has retrieved the log page includes querying all controllers to verify that the AEN sending is enabled. 
     
     
       14. The federated multi-appliance data storage system of  claim 8 , wherein the migrating is performed as part of a migration session, and upon creation of the migration session, (1) the host computer's connectivity to the second data storage appliance is checked prior to the synchronizing phase, to ensure that controllers exist on the second data storage appliance and have been discovered by the host computer, and (2) the destination virtual volume is created without mapping it to the host computer, so that the destination virtual volume remains inaccessible to the host computer until the cutover operation.